Valves

ABSTRACT

A method whereby the distribution device of a valve constituted by a train of valve-discs mounted on a common valve-stem is put in a preferential position, this position being attained by utilizing the pressure of the liquid which is present within the distribution device, said pressure being exerted independently of the operating means of the distribution device, on the complete valve train in order to subject this latter to a resultant force which always has the same direction. All the valve-discs which form part of the distribution device including the drain valve are grouped together on a common stem; the valve-discs are suitably dimensioned with respect to each other and the flow and leakage cross-sections are also suitably dimensioned; the forces arising from the flow of hydraulic fluid which are thus obtained tend to bring the distribution device into its predetermined preferential position.

United States Patent Launay et al. I

[ VALVES [72] Inventors: Jacques Launay, Colombes; Jacques Mongault, Paris, both of France [73] Assignee: Permo, Saint-Cloud, France [22] Filed: Nov. 3, 1970 [21] Appl; No.: 86,462

[30] Foreign Application Priority Data Nov. 3,1969 France .6937680 521 u.s.c1 ..l37/625.5,2l0/278 511 1111.0. ..Fl6k 11/02 581 Field 6rsear6h...210/190, 191,278; 137/625.5,

[56] References Cited UNITED STATES PATENTS 1,679,614 8/1928 Lichtenberg ..l37/625.27X 2,741,264 4/1956 Leonard ..l37/625.5 3,138,553 6/1964 Mollring ..210/191x [151 3,683,961 [4 Aug. 15, 1972 Primary Examiner-Henry T. Klinksiek Attorney-Michael S. Striker [57] ABSTRACT A method whereby the distribution device of a valve constituted by a train of valve-discs mounted on a common valve-stem is put in a preferential position, this position being attained by utilizing the pressure of the liquid which is present within the distribution device, said pressure being exerted independently of the operating means of the distribution device, on the complete valve train in order to subject this latter to a resultant force which always has the same direction. All the valve-discs which form part of the distribution device including the drain valve are grouped together on a common stem; the valve-discs are suitably dimensioned with respect to each other and the flow and leakage cross-sections are also suitably dimensioned; the forces arising from the flow of hydraulic fluid which are thus obtained tend to bring the distribution device into its predetermined preferential position.

1 1 corms, 14 Drawing Figures Patented Aug. 15, 1972 3,683,961

3 Sheets-Sheet 1 g Q' Q1 wi Inuit- F: 14:0": Mum? 14 on I. (M ff/hw Patented Aug. 15, 1972 3 Sheets-Sheet 5 FIG-,3

KM /A VALVES This invention relates to valves, in particular to valves which are primarily intended for use in conjunction with equipment units for the treatment of liquids such as units for water treatment and especially in association with water softeners, sand-filters or granular material-filters, units for demineralization on resin, water supply systems and so forth. The invention is more especially concerned with automatic valves for carrying out a sequence of operations.

The different types of valves which are known at the present time are distinguished by the number of periods or the number of positions taken up successively in order to establish the communications which are necessary according to the particular application under consideration.

In the case of each type of valve, the liquids to be treated can be conveyed in the intended direction by means of systems or devices suchas distributing valves of the rotary type, displacement type, diaphragm type,

gate type and so forth, all of which carry a certainnumber of disadvantages, the most common of these being the following:

a large number of components the need of accurate machining long assembly time and high cost price delicate mechanisms wear which is liable to result in faulty operation and defective leak-tightness use which is limited to a narrow pressure range substantial pressure drops substantial overall size.

The general trend towards simplification of mechanisms in present-day techniques leads to the need for an in-line arrangement of the chambers or communication means which form part of a valve and which have to be shut off as a function of the operating cycle of the valve considered.

Among the valves which are constructed in accordance with this design concept, the following may be mentioned:

on the one hand the valves whose positions are taken up successively under the action of hydraulic pressures which produce action both on the valve-discs and on the piston or operating diaphragm which are associated with these latter, the said valves being set in operation by means of a valve-disc which shuts off the drain outlet and is separate from the moving system;

on the other hand, the valves in which all the discs as well as the drain valve are grouped together on the same shaft (or so-called valve-stem) but in which the positions taken up successively result from the mechanical action of an external element which is coupled to the moving system;

finally, valves in which all the discs are mounted together on the same stem but in which the open-' ing of one port can be effected only after closure of another port.

In the first case, the final aim has not been fully achieved inasmuch as one of the closure members or discs which governs the operation of the valve is dissociated from the moving system and complicates the mechanism. 7

Similarly, in the assembly which is met with in the second case, a number of valves are intended to provide a simultaneous tightness on a number of seats but this can never be achieved in a wholly satisfactory manner without a complex arrangement of the moving system which consists of valve-discs, circlips, springs and which is actuated by an external mechanism comprising a restoring means.

The arrangement which is found in the third case entails the use of sliding valves, the displacement of which is partly obtained by means of a spring and partly with the aid of a double-acting external control means.

Up to the present time, it had not proved feasible to propose a valve in which the distributor or distributors grouped together without exception all the valves which are necessary for the application under consideration and in which the successive displacements of said distributors are carried out with the aid of single acting operating means without the addition of any restoring device proper.

The object of the present invention is to make provi sion for automatic valves of simplified type which meet practical requirements more effectively than comparable valves which were employed for the same purpose in the prior art, especially insofar as the valves according to this invention have a small number of components, do not call for a very high degree of accuracy in molding or machining dimensions irrespective of the material of which they are formed and permit a reduc tion both in time of assembly and in capital outlay; moreover, the valves in accordance with the present invention are of strongly built design and of small overall size; they have only a small number of moving parts, the effect thereby achieved being to eliminate causes of wear and to ensure a high degree of leak-tightness in all successive positions; they can be employed over a wide pressure range and also provide an entirely free passageway resulting in minimized pressure drops.

This invention is directed to a method whereby the distribution device of a valve constituted by a train of valve-discs mounted on a common stem is put in a preferential position, said method being essentially characterized by the fact that said preferential position is attained by employing the pressure of the liquid which is present within the distribution device, said pressure being exerted independently of the operating means of the distribution device or of any auxiliary means, on the valve train taken as a whole in order to subject said valve train to a resultant force which always has the same direction.

in accordance with the invention, the means adapted to carry out said method consist in the fact that the pressures which are exerted on the valve train by the liquid within the distribution device and which subject said valve train to a force which always has the same direction are obtained by grouping together on a common stern all the valve-discs which form part of the distribution device including the drain valve, as well as by suitable dimensioning of the valve-discs with respect to each other and of the flow-and leakage-cross-sections which generate forces arising from the flow of the hydraulic fluid and tend to bring the distribution device into its predetermined preferential position.

This invention further relates to an automatic valve which is primarily intended for use in conjunction with equipment units for the treatment of liquids and especially water treatment units. Said valve essentially comprises a distribution device equipped with a train of valve-discs including the drain valve which are mounted on a common stem, and suitable flowand leakage-cross-sections which are dimensioned in a predetermined manner as hereinabove defined.

According to one advantageous embodiment, the positions which are taken up successively by a train of valve-discs establish in alternate sequence a connection and separation between the chambers in which said valve-discs shift and the chambers which are located on each side.

According to another advantageous embodiment, a plurality of valve-discs can open or close a single port which provides a communication between two chambers.

In accordance with a further embodiment, the valvediscs are mounted in such a manner as to permit of sliding motion on the valve-stem while retaining leaktightness between said discs and said stem.

In again another embodiment, the valve-discs are formed of sufficiently flexible material such as rubber, for example, in order to ensure sufficient leak-tightness within the desired pressure range while being applied against the seats of the ports to be shut off.

In an arrangement of this latter embodiment which is conductive to enhance leak-tightness, a slot is formed in the flexible material from which the valve-discs are fabricated.

According to yet a further embodiment, the valvediscs are formed of a rigid material or provided with a rigid strengthening core.

According. to still a further embodiment, the valvediscs have different cross-sectional areas.

In a preferred arrangement of this latter embodiment, the leakage-cross-section' of the valve-discs which have a large sectional area is smaller than the leakage-cross-section of the valve-discs which have a smaller sectional area.

In accordance with another advantageous embodiment of the invention, the valve-discs are maintained A better understanding of the invention will be obtained from the following complementary description,

. reference being made to the accompanying drawings in on the stem by any suitable means such as shoulders formed on said stem or grooves formed-therein; said discs may also be provided with retaining shoulders only on one side. In accordance with a particular mode of assembly of the discs on the valve-stem, said discs are capable of displacement within different bores but without being applied against seats in order to establish connections between different ports.

In accordance with a preferres embodiment of the invention, leak-tightness between each valve-disc and the stern on which said discs are mounted is obtained which a two-stage valve for a softener unit is illustrated by way of non-limitative example, and in which:

FIG. 1 is a sectional view of a two-stage valve in accordance with the arrangements of the invention;

FIG. 2 shows a distribution device in which thevalvediscs are capable of relative displacement as a result of simple sliding motion;

FIG. 3 is a sectional view showing a valve train comprising a disc of the rigid type and a deformable disc of the flexible type;

FIGS. 4 and 5 show diagrammatically the means for operating the distribution device in accordance with the invention;

FIG. 6 is a sectional view of an alternative form of two-stage valve as constructed in accordance with the arrangements of the invention;

FIG. 7 is a part-sectional view showing the leakagecross-sections and the guiding of the distributor onto a drain seat;

FIGS. 8 and 9 show diagrammatically the deformation to which the valve-discs can be subjected in order to ensure effective leak-tightness at several levels;

FIG. 10 shows another guiding means;

FIG. 11 shows a distribution device comprising five valve-discs in different alternative forms of construction;

FIGS. 12 and 13 show the positions taken up successively by a valve train which establishes in alternate sequence a connection (as shown in FIG. 12) and a separation (as shown in FIG. 13) between the chambers within which said valve-discs travel and the chambers which are located on each side;

FIG. 14 shows one form of construction of the distribution device in accordance with the invention in which a plurality of valve-discs are capable of either opening or closing a single port which provides a communication between two chambers.

It will be understood that both the drawings and corresponding parts of the description are given primarily in order to explain the object of the invention and are not intended to imply any limitation whatoever.

In valves for softener units involving two-stage regeneration, there is a utilization position and a regeneration position.

In the utilization position, the valve serves to pass the raw water to be treated through an ion-exchange resin bed and to fill at the same time a salt storage tank in order to form the brine which serves to regenerate the resins when these latter are depleted.

In the regeneration position, the valve serves to feed the raw water through a by-pass to a hydro-ejector which draws in the brine in order to pass this latter through the resin bed in the direction which is reverse to the utilizationdirection and to regenerate the bed until no brine remains, whereupon the resin bed is rinsed with the driving water of the hydro-ejector and again in the same reverse direction, the brine as well as the rinsing water being discharged to waste throughout this operation.

In accordance with the invention, it is merely neces-' sary to exert a greater effort in the direction opposite to that which maintains the distribution device in a preferential manner in order tochange over from one position to another.

The distributor remains in its new position as long as the effort is maintained and returns automatically to its initial position as soon as said effort ceases.

It is readily apparent that the force which serves to displace and maintain the distributor in all the positions other than the preferential position can be of any kind such as pneumatic, hydraulic, mechanical, electrical and so forth.

In all cases, the element which exerts the operating effort on the distribution device is not necessarily coupled mechanically therewith; it is only necessary to ensure that said element should be applied against. the device inasmuch as the operating force is exerted only in one direction and has no other effects.

If so required, it is also possible to employ the hydraulic and automatic return of the distribution device in order to restore or even to re-actuate the operating means.

According to a particular design concept of the valve as contemplated by the invention, the valve train which constitutes the distributor could change over from one end position to another in successive forward movements corresponding to weIl-determined'intermediate positions, in which case the return takes place in ac- A diaphragm 10 which is secured tothe actuating stem 13 by means of the abutment member 14 and clamped between the body 1 and the block 2 constitutes movable divider means and ensures leak tightness between the compartments 11 and 23.

The reduction-gear motor 3 which is fixed on the block 2 produces action on the jack or valve member 12 by means of the cam 15, the raw water is admitted through the port 16, circulates through the valve via the duct 17, passes through the resins and then the softened water is then conveyed through the duct 18 so as to pass out for utilization through the port 19. The valve-disc 8 ensures leak-tightness against the seat 5, thereby cutting off any direct communication between the inlet 16 and the outlet 19. In this position, the valve-disc 9 ensures leak-tightness against the seat 7 and prevents any communication between the inlet 16 and the drain outlet 20. However, the duct 21 is in communication with the chamber 31 of the control jack 12 which, as shown in FIG. 4, causes the valve disc 29 to be applied against the seat 30, thereby cutting off any communication withthe compartment 11 as a a result of the pressure of the supply system, said comcordance with the same criteria up to the preferential end position.

In accordance with the invention, the valve train can comprise an unlimited number of valve-discs.

Similarly, a valve inaccordance with the arrangements of the invention can be constituted by a combination of several distribution devices which may be either dependent or independent of each other.

In accordance with one advantageous solution, a diaphragm applied against the extremity of the device which carries the thrust is employed as operating means. The applicationof pressure to said diaphragm which has the effect of producing the desired effort can advantageously be initiated by an electric reductiongear motor which drives a cam and thus actuates a hydraulic control jack having the characteristics disclosed in the co-pending US. Pat. application Ser. No. 84,773 as filed in the name of the present applicants on Oct. 28, 1970 and entitled Improvements to control devices for pressure chambers."

A further solution consists in replacing .the diaphragm by a piston which is displaceable within a cylinder or by a push-rod, lever, control member, spring or the like which produces action on the distributor.

Triggering of said operating means can be performed manually or rendered automatic by means of a timedelay system, clock or the like which actuates a hydraulic or pneumatic electrovalve or alternatively an electrical or mechanical device and so forth.

In accordance with the invention, the flow path followed by the liquid through the valve is modified by the translational motion of the distribution device.

As shown in FIG. 1', the two-stage valve in accordance with the present invention consists of a body 1 which comprises in coaxial relation the stepped valve-seats 4, 5 and 6, 7 between which the shut-off valve-discs 8, 9 move respectively and are mounted on the shaft or stem 13.

which has the effect of displacing the stem 13, thereby moving the valve-discs 8, 9 towards the seats 4, 6 of the body 1. There is then established a direct communication between the inlet 16 and the outlet 19, i which makes it possible to draw off raw water via the by-pass y from theoutlet of the or brine producing means 35 and the operation of this latter is thus carried out by supplying the driving water through the port 34.

The brine which is thus drawn in passes through the resins in the direction opposite to that in which the water circulates during the softening stage. Said brine follows the duct 18, then the duct 17 and is discharged through the drain outlet 20 after having passed through the compartment 23 in which the flow is practically gravitational. When the cam 15 no longer produces action on the jack 12, the pressures of the supply system which act on the cross-section of said jack close the valve-disc 29 again and uncover the duct 22; the compartment 11 is thus drained-off through the ducts 32, 22. In fact, any operating or retaining effort on the distribution stem 13 is stopped.

Under these conditions, the choice of flow or leakage cross-sections produces drops in pressure at the time of flow of the liquid.

This results withinthe interior of the distributor in different pressures in the different chambers. These pressures are applied to the valve-disc faces and exert efforts which are proportional to the surface areas of said discs. 9

By virtue of a suitable choice of the disc surface areas and of the internal pressures, the resultant of said efforts is continuously in the same direction irrespective of the position of the valve train.

Moreover, if the flow of fluid is stopped, which can only occur in the utilization position, the internal pressures are equal but the choice of cross-sectional areas of the valve-discs 8, 9 always maintains the resultant of the efforts in the same direction. This result is therefore obtained solely by utilizing the pressure of the liquid which is conveyed within the distributor; and the distribution stem 13 returns automatically to the utilization position which has been given as the preferential position.

The abutment member 14 is applied against the base of the block 2 and thus limits the travel of the diaphragm 10 after having produced the sliding motion and deflection of the valve-discs 9, 8 which have been applied against their respective seats 7, 5 and ensures leak-tightness between the compartments or ports l6, l9, and 16, 23 respectively; the valve then no longer produces any leakage to waste and the raw water is delivered through the outlet 19 after having been softened.

In an alternative form of two-stage valve' in accordance with the invention as illustrated in FIG. 6, the diaphragm 110 is not directly attached to the distribution stem 113 but is only applied against this latter when the chamber 1 11 is put under pressure.

Moreover, the bearing 136 which is located within the seat 105, which separates the chambers 119 and 116 serves to guide the valve-stem at its center. As indicated in FIG. 7, the seat 107 has also been employed for the purpose of guiding the extremity of the distributor; a number of milled grooves 137a, 137b, 1376 have also been formed in said extremity in order to permit the liquid to flow from the chamber 1 17 to the chamber 123 when the valve-disc 109 is not applied against the seat 107. The total cross-sectional area of said milled grooves is intended to be smaller than the cross-sectional area of the port 120 which serves to discharge the chamber 123 to waste.

In another alternative form shown in FIG. 10, the stem 113 is guided at its extremity 138 within a bearing 139.

It can more readily be understood from FIGS. 8 and 9 that the valve-disc 108a is capable of deformation when the valve-disc 109a is displaced between the seats 107a and 106a provided that the permissible displacement between the seats 104a and 105a is intended to be smaller than that which takes place between the seats 107a and 106a.

FIG. 3 clearly shows the difference which can exist between valve-discs 9b of the rigid type and the valvediscs 8b of flexible material; if so required, said valve discs 9b can serve to limit the ranges of travel of the stem and of the valve-discs of type 8b in which a nick 26 has been cut for enhanced flexibility.

According to a further embodiment which is illustrated in FIG. 2, the valve-discs 8a and 9a are capable of sliding along the stem 13a in order to compensate for differences between their respective ranges of travel which may result from defective machining of their respective seats with respect to the displacement carried out by the distributor stem itself.

The practical effect of this arrangement is to ensure correct leak-tightness by compensating for any possible variation between the travel of the valve train and the distance between the seats against which valve-discs are applied.

In another alternative arrangement, there can be devised for a different type of valve a distribution stem fitted with a number of stepped valve-discs 208a, 208b, 208c and 209, 209a which are maintained in a fixed manner on the shaft 213 between different annular shoulders 239a, 23% and 239C and 239d, the distributor being guided at its extremities and more particularly by means of an extension 238.

In an advantageous arrangement of the invention, the valve train can establish in alternate sequence a connection and a separation between the'chambers in which the valve discs travel and the chambers which are located on each side; the positions which are accordingly taken up in turn by the valve train are shown respectively and diagrammatically in FIGS. 12 and 13.

In addition, FIG. 14 also shows diagrammatically the arrangement of the invention in which a plurality of valve-discs can either open or close a single port which is in communication between two chambers.

It follows from the foregoing description that, no matter what modes of construction and application may be adopted, the automatic valves which are thus obtained and employed in conjunction with equipment units for the treatment of liquids offer substantial advantages over valves of this type which were known heretofore and in particular the following:

the assembly of a train of valve-discs on a common shaft as contemplated by the invention results in simplification of manufacture. This makes it possible in particular to obtain the main components which constitute the valves in accordance with the invention by molding of plastic material, for example, without entailing any precision either in machining, molding or assembly. This in turn makes it possible to employ as-molded parts of plastic material in particular and results in the production of valve units which are low in capital cost.

the possibility of manufacturing the train of valvediscs and the valve-stem by molding in one piece dispenses with the need of springs for retaining the valve-discs, said springs being both cumbersome and liable to give rise to fault conditions as was the case with the assemblies which were in use in the prior art.

by mounting a train of valve-discs on the same stern,

there is no longer any need to mount separate valves in accordance with the practice which was prevalent heretofore and which entailed the use of a number of control devices corresponding to the number of valve-discs.

Finally, in addition to the very appreciable reduction in the cost price of the valves according to the invention, the simplification which is achieved in the manufacture of these valves and which includes simplification of assembly and control also secures the advantage of very high operational safety and reliability.

As has been brought out by the foregoing, the invention is not limited in any sense to those modes of construction and application which have been more specifically described but extends to all alternative forms which may be conceived by any one versed in the art without thereby departing either from the scope or the spirit of the invention.

What we claim is:

1. A valve comprising a valve housing forming a first pair of spaced annular valve seats and a second pair of spaced annular valve seats all aligned along a common axis, an inlet port between adjacent valve seats of said first and second pairs, an outlet port between said first pair of valve seats, a first fluid flow passage providing communication between said inlet and said outlet port through said adjacent valve seat of said first pair, a second flow passage leading from said inlet port through the adjacent valve seat of said second pair, the space between said second pair of valve seats and through the other valve seat of said first pair to said outlet port, and a third flow passage providing communication between the space between said first pair of valve seats and said second flow passage, and a chamber laterally of the other valve seat of said second pair of valve seats; a first valve disc between said first pair of valve seats and a second valve disc between said second pair of valve seats; a common valve stem carrying said valve discs for movement between the respective valve seats, said valve stem having an extension extending through the other valve seat of said second pair into said chamber, one of said valve discs being connected to said stem for movement therewith in at least one direction and the other of said valve discs being connected to said stem at least for movement in the opposite direction, said chamber having a cross-sectional normal to said axis which is greater than the cross-section of each of said valve discs; movable dividing means extending transversely through said chamber and dividing the latter into two compartments, said extension of said valve stem abutting with a free end thereof against said dividing means; a drain outlet communicating with one of said compartments; and operating means movable between a first and a second position for connecting in said first position said two compartments with each other and therewith to said drain outlet so that the pressure of the fluid passing through said inlet port into said valve housing will move said second valve disc into engagement with the other of said second pair of valve seats and said first valve disc into engagement with the adjacent seat of said first pair of valve seats while moving said stem and said dividing means in a first direction whereby fluid will flow from said inlet port through said second flow passage to said outlet port, and for connecting in said second position said inlet port with the other compartment while interrupting communication between said compartments so as to move said dividing means and therewith said stem in a second direction opposite to said first direction while said second valve disc is moved in engagement with the adjacent valve seat of said second pair and said first valve disc in engagement with the other valve seat of said first pair of valve seats whereby part of the fluid entering through said inlet port will flow through said first flow passage and another part through said third flow passage, said second flow passage and said other valve seat of said second pair into said one compartment and leave the latter through said drain outlet.

2. A valve as defined in claim 1, wherein said movable dividing means comprises a flexible diaphragm exte ifiiiiaifiifi c fil rll i tili ilh said extension is fixedly connected to said diaphragm.

4. A valve as defined in claim 1, wherein said first pair of annular valve seats of said first valve disc have a diameter smaller than that of said. second pair of annular valve seats and said second valve disc.

5. A valve as defined in claim 1, wherein said first valve disc is fixed to said valve stem for movement in either direction with the latter.

6. A valve as defined in claim 5, wherein said first valve disc is made from resilient material and formed with an annular groove extending inwardly from the peripheral surface thereof to a diameter smaller than the inner diameter of each of said first annular valve seats.

7. A valve as defined in claim 1, wherein said extension has a diameter greater than the remainder of said stem so as to form a shoulder abutting against said second valve disc at least when the latter abuts against said adjacent valve seat of said second pair of valve seats.

8. A valve as defined in claim 1,, wherein said operating means comprises auxiliary valve means and means cooperating with said auxiliary valve means for moving the same between said first and said second position.

9. A valve as defined in claim 1, wherein said valve housing is formed with a bore forming at one end an additional valve seat, an additional chamber adjacent said valve seat and communicating with said inlet port, and a pair of fluid passages respectively providing communication between said compartments and said bore, and wherein said operating means comprises an auxiliary valve member movable in said bore and carrying at one end thereof extending in said additional chamber an additional valve disc adapted to engage said additional valve seat, said valve member having spaced from said one end a large diameter portion sealingly engaging said bore and between said additional valve disc and said large diameter portion a smaller diameter portion to define with the inner bore surface an annular space,

said valve member being normally held in said first position by the fluid pressure in said additional chamber in which said additional valve disc engages said additional valve seat and in which said annular space provides communication between said pair of fluid passages and therewith between said chambers, and including means for moving said valve member from said first to said second position in which said additional valve disc is spaced from said additional valve seat and said large diameter bore portion of said valve member interrupts communication between said pair of fluid passages.

10. A valve as defined in claim 9, wherein said moving means comprise means for cyclically moving said valve member from said first to said second position.

11. A valve as defined in claim 1, and including an ion exchange resin bed in said second fluid flow passage and brine producing means in said third fluid flow passage. 

1. A valve comprising a valve housing forming a first pair of spaced annular valve seats and a second pair of spaced annular valve seats all aligned along a common axis, an inlet port between adjacent valve seats of said first and second pairs, an outlet port between said first pair of valve seats, a first fluid flow passage providing communication between said inlet and said outlet port through said adjacent valve seat of said first pair, a second flow passage leading from said inlet port through the adjacent valve seat of said second pair, the space between sAid second pair of valve seats and through the other valve seat of said first pair to said outlet port, and a third flow passage providing communication between the space between said first pair of valve seats and said second flow passage, and a chamber laterally of the other valve seat of said second pair of valve seats; a first valve disc between said first pair of valve seats and a second valve disc between said second pair of valve seats; a common valve stem carrying said valve discs for movement between the respective valve seats, said valve stem having an extension extending through the other valve seat of said second pair into said chamber, one of said valve discs being connected to said stem for movement therewith in at least one direction and the other of said valve discs being connected to said stem at least for movement in the opposite direction, said chamber having a cross-sectional normal to said axis which is greater than the cross-section of each of said valve discs; movable dividing means extending transversely through said chamber and dividing the latter into two compartments, said extension of said valve stem abutting with a free end thereof against said dividing means; a drain outlet communicating with one of said compartments; and operating means movable between a first and a second position for connecting in said first position said two compartments with each other and therewith to said drain outlet so that the pressure of the fluid passing through said inlet port into said valve housing will move said second valve disc into engagement with the other of said second pair of valve seats and said first valve disc into engagement with the adjacent seat of said first pair of valve seats while moving said stem and said dividing means in a first direction whereby fluid will flow from said inlet port through said second flow passage to said outlet port, and for connecting in said second position said inlet port with the other compartment while interrupting communication between said compartments so as to move said dividing means and therewith said stem in a second direction opposite to said first direction while said second valve disc is moved in engagement with the adjacent valve seat of said second pair and said first valve disc in engagement with the other valve seat of said first pair of valve seats whereby part of the fluid entering through said inlet port will flow through said first flow passage and another part through said third flow passage, said second flow passage and said other valve seat of said second pair into said one compartment and leave the latter through said drain outlet.
 2. A valve as defined in claim 1, wherein said movable dividing means comprises a flexible diaphragm extending transversely through said chamber.
 3. A valve as defined in claim 2, wherein said extension is fixedly connected to said diaphragm.
 4. A valve as defined in claim 1, wherein said first pair of annular valve seats of said first valve disc have a diameter smaller than that of said second pair of annular valve seats and said second valve disc.
 5. A valve as defined in claim 1, wherein said first valve disc is fixed to said valve stem for movement in either direction with the latter.
 6. A valve as defined in claim 5, wherein said first valve disc is made from resilient material and formed with an annular groove extending inwardly from the peripheral surface thereof to a diameter smaller than the inner diameter of each of said first annular valve seats.
 7. A valve as defined in claim 1, wherein said extension has a diameter greater than the remainder of said stem so as to form a shoulder abutting against said second valve disc at least when the latter abuts against said adjacent valve seat of said second pair of valve seats.
 8. A valve as defined in claim 1, wherein said operating means comprises auxiliary valve means and means cooperating with said auxiliary valve means for moving the same between said first and said second position.
 9. A valve as defined in claim 1, wherein said valve housing is formed with a bore forming at one end an additional valve seat, an additional chamber adjacent said valve seat and communicating with said inlet port, and a pair of fluid passages respectively providing communication between said compartments and said bore, and wherein said operating means comprises an auxiliary valve member movable in said bore and carrying at one end thereof extending in said additional chamber an additional valve disc adapted to engage said additional valve seat, said valve member having spaced from said one end a large diameter portion sealingly engaging said bore and between said additional valve disc and said large diameter portion a smaller diameter portion to define with the inner bore surface an annular space, said valve member being normally held in said first position by the fluid pressure in said additional chamber in which said additional valve disc engages said additional valve seat and in which said annular space provides communication between said pair of fluid passages and therewith between said chambers, and including means for moving said valve member from said first to said second position in which said additional valve disc is spaced from said additional valve seat and said large diameter bore portion of said valve member interrupts communication between said pair of fluid passages.
 10. A valve as defined in claim 9, wherein said moving means comprise means for cyclically moving said valve member from said first to said second position.
 11. A valve as defined in claim 1, and including an ion exchange resin bed in said second fluid flow passage and brine producing means in said third fluid flow passage. 